Process of correcting photographic copies for facsimile transmission



pra 22, 1930.

R. H. RANGER PROCESS OF' CORRECTING PHOTOGRAPHIC COPIES FOR FACSIMILETRANSMISSION Filed Augf24, 1925 TTORNEY RICHAIBD EOWLAN D RANGER,

vInitted which is adapted to give the best re- Patented Apr. 22,' 1930TES* lrrr Fri PORATION Oi AMERICAVA .CORPORATION 0F DELAWARE raoonssrorOonREcrINe PHOTOGRAPHIO' COPIES non FACSIMILE rannsmissmt" Appncafi'onmea August 24, 1925. serial NQ.- 51,930.

This invention relates to certain new and useful improvementsin thetransmission of facsimile'messages, and more especially to a process forimproving the detail of transmitted facsimiles' and toa process forproducing a 'film of the facsimile to be transsults, particularlywhenthe transmission is carried on according to the method disclosed andclaimed in my copending application,

` Serial No, 726,235,led July 16, 1924 forA Duplex photo modulator-7.

ln the said application-l have shown a method and apparatus wherebyvariations of light intensityl correspondingto successive areas fof thefacsimile to 4be ltransmitted are translated into impulses varying inlengt or spacing according to light intensity.

lt hasbeen found that in -general films' which are supplied :to betransmitted vary greatly', not only yin light intensity, but in therange of light intensityvvhich may be covered by the'high lights andshadows of particular pictures. For example, to express this lin aquantitative vvay.'if We designate the intensity of light falling onthelm by L0 'and the intensity o`f light transmitted transmitted throughit be substantially equal to that falling upong i t and the l ratio inthis case Will have avalue of unity.VY If, on the other hand, the lm islvery dark, for i instance almost black, the lighttransmitted throughthe film maybe onlyperhaps 1/100.

' of the light falling upon'it and the ratio in this case would be100.vFor certainzpurposes it is desirable to con- Sider, not this ratioitself, but they logarithm ofthis ratio to the base 10, which istermedldensity.

From the foregoing, it will beunderstohdthat a'film of zero density isafilmfvvhich'is perfectly clear and thatv aiilm of'2.'0 density ispractically Opaque.' 'It will'also be. seen 'to produce a film thatintermediate values ofthis density will lie along a logarithmic scalefrom opaque to clear. l

or, BROOKLYN, NEW YORK, Assienon, 'ro RADIO com ln carrying out thetransmission 'of facsimiles, and more particularly pictures, in.

accordance with my invention above referred mitted equally Well, butthat the best results lare obtained by the 'use of what may be termed lathin lm;'that is to say, O ne in vvhic'h the Opacity is relatively low,through- 'out the picture 4and vin which the density varies 'between0.1 and 0.8 approximatelygior in other' Words, a standard picture or lm.As a rule, photographic films. do not fall within this range, but. areno rmally'much to, I have found that 4all Vlms'arfe not trans'- moredense both in highlights and shadows y and likewise they average rangeofl density,k

or the contrast, is greater.

- If such films werevtransmitted, a certain amount of detail Would'-therefore be `loste fre To obviatethis, in accordance with my in?vention l: produce from the iilm tofbe transmitted acopy falling Withinthe range desired. It 'might' of course be possible to produce a copyhaving the desired -range by a method of cut and"try.""r4 This'however fwould be uneconomical and ineliicient and I;

have therefore ,devised a method and appa-V ratus for determininglirst'of all the dented, and secondly for determining under 'whatconditions the copyingof the should b e `carried' out to produce a ilmhavlng the density range foun by eXpeen-r .tobebestb l v y.

` .In v ievv of theYA foregoing, it will now'be understood that it isanobject' of this inven'- tion to produce a method and apparatusrforutilizing afacsimile transmission system to,l

the best advantage.

mi, vsity range of any lm desired to be transmitltis a further objectofl this invention producea method and `'apparatus whereby p any-51m maybe'copied to producea film lying Within a predetermined density range.

to produce amethod and apparatus fonelimillt is a-lfurtherlobject ofthis invention natingguess 'Work and Wastage in atted ipting; l

range.

having a ldesired densityw StillV further objects of my inv'ention Willhe apparent lfrom the specification.

My inventi'onvvill` best be understood. by reference'to the vfollowingdescription taken in connection 'With the; accompanying ldrawing,invvhichz-f` F ig. lis a reference chart used in carrying 4out myinvention, and

.F ig. 2 is a curve showing the rangeV of contrast of variousphotographic materials.

ln accordance with, myjinvention, I iiist take'thg' film which itisdesired to transmit rand' measure its density range on What may betermed a densitometeinA The precisel construction and arrangement 4of adensitometer forms no part of this invention.` 'A. suitable densitometermay consist of a standard light focusing its beam on a calibratedmeasuring scale having a variety of densities or on the lm to bemeasured. This light beam is then thrown by suitable optical means on aphoto Acell andthe current variations produced'by changes in lig-htintensity are applied to the Agrid 1ofa three-electrodevacuum tube insuch a manner as to cliange'the gridvoltage of this tubeand consequentlythe plate .current from which the density may be determined bycomparisoii With the standard densities.

Having determined as distinguished from merely estimating, the densityrange .of the film .desired to be transmitted, We may proceed to 'copyit in such amanner as to give the desired density range in the copy, as'will be more particularly described. i have found that the density rangein any film copyis dependentupon a number of factors, for example, timeof lexposure, time of development, type of film, etc.' The slower typesof film result in a. copy having` a'inuch greater rang ofdensity than afast iil'm for the normal exposure for each type.

Also, it Will be found that short exposures of *varying light intensitywill give arange of density values different from long exposures of thes amevarying light values. in general 7 it Will be found that the longerthe exposure from a light' of a given' intensity, the greater will bethe density of all parts of the picture and for a very extreme exposurethe film could be converted into a uniformly opaque layer. Y

Thedifierent'in .intensity-.between the portion' of the fi'lm receivingthe strongest illumi-,. nation and the portion receiving the Weakest fillumination depends upony the 'lengthof time sof development. .it Visfoundthat vvith'a given exposure a short'time'otdevelopment will.produce acertain density in vthe por- 'tions'receivingthe leastliglitand a'greater density in" the port-ions receiving the most iight. inincrease in development time will` produce agreat-'er` density in theportions receiving theleast light and a proportionately' `much greaterdensity in the portions' r eceivl ing the mest light. lt is, theretere,'possible bei f to control the range of contrast between the maximum andminimum densities of the lm by a variation in development time.

part of the film or the average density by var i. 'the ex'iosure.

From this it Will be seen that by varying the iength'ofr time ofexposure and the length oftime4 of development the density range and themaximum and minimum densities can be ,brought to adesired value.

For instance, referring to Fig. l, in which it is also 'possible tovcontrol the density of any given abscissae designate maximum densityand ordinate designate minimum density, it will be seen that to 'obtaina iilm of the desired range from a film havinga maximum density of .60'land a minimum-density of .10,A -it is necessary to give a two secondsexposure and to develop for five minutes. On the other hand, to obt'ainafilm of the desired range from a. film having a maximum density of 1.0,and a minimum densityof'l, it is necessary to' give an exposure of 32seconds, greatly in excess of that required forthe first example. vToprevent shifting the Whole film ldown the scale towards black,development time is only two minutes, as will be seen.

To give` another example, suppose it is de- -sired to produce afilm fortran'smissionfrom a film having a maximum density of .TO and a minimumdensity of .10, by reference to the chart it Will be seen that a fourseconds exposure is'required'and fear minutes development. On the otherh'and', if the film to be copied-has a maximum density of .'i'Ofan-d aminimum densityof .30 only'tivo seconds exposure is required, but l0minutes development is necessary.

The examples just given andthe blocks on the chart of F ig; Lin which nofilm is mentioned are 'given for Eastman Process Films and EastmanProcess Developer at a tempei'- l ature of TO Fahrenheit with.cameralens however. be reproduced togive a satis-` factory film fortransmission by choosing an-l other type of sensitized film. Forinstance .for a film having a maximum density of 1.20

and a minimum of .20,-an Eastman commercial film may be used giving it.three seconds,

exposure and three minutesu development.

Vlhe'factois governing the choice of 'lm to be made to secure a suitablereproduction are indicated by lthe curves of Fig. 2 which show thedifterence in density obtained in the completed copyfrom a givenoriginal when dit- 'fer'ent types of film are used.- From 'thesecurves`itv Will be evident that a certain? film marked A would give onlya very small range ofideii'sity when the original from' lil CII

. which the copy .is madehas `a Wide range of' lowest contrastoriginals, such as isshown for making the copy..

instanceby the use of Peerless. 'ilni for an original having amaximumdensity of- 1.0

and a minimum density of 5'5.' Also,'-it may j y e .electricaltransmission and facsimile thereof,

be stated that special ranges maybeitaken care of by Vvaryingthetaperture ofthe lI 1 S,,I.1

while 'r have diseased Aan .anime .the methodof preparing pictures for.electrical transmissiomit is'to be distinctly understood" vthat thelsubject matter transmitted-mayv be in addition'to pictures,checks,.fnger prints,

financial' statements, newspaper; articles, mo-f `tionpicturefil'ms andthe like, rand, infact,

all other matter which iscapable of'bein'g Y readg'or .viewed bythe eye,and, therefore, I'believe thatthe term.pictur elf, as used throughout.-the' specification and claims,

` should be "broadly construed. and considered as broadly relating toall of the, various `steps claims.

to be. hereinafter defined and .set forth."

While I -havc shown b'utga single embodi-A ment of the method of myinventiomit'is capable of modifications therefrom and it isdesiredtherefore y that only such limitations f shall be imposed thereon 'asare required'by the'prior art or indicatediby the appended claim:v je. 1. The method-of preparing a picture for'.- electrical transmissionof a fascimlle thereof, f

which comprises, optically determining the.

average density range of sai'd'picture, 'coni-1 paring saidpicturelwith" a predetermined: schedule of denstyrrangef'obtained -froma" 3. The method of pre ari-nga ictlnrfla'for of a facsimile thereof,

standard picture having an optimum den- 'fsity range for electricalfacsimile transmis#` sion, determiningthe ratio of 'density ra-ngebetween said'picture and said standard. from said comparison,reproducing.. said'. rst

named picture-to vsecure a copyjthereof havlng with the said ratio, andelectrically imansnnts"V ting a .facsimile of saidcopy.

4c.. The method of preparlng a picture for a 'density range varying inaccordance y optimum range fofdensityin 'a' standard pic-v' j 'ture 'forelectrical facsimile` transmission,

optically measuring the rangefof density kin a second picture tcb'etransmitted, determining the ratio ofthe respective ranges of light lintensities insaidpictures, producing. a copy of -saidsecond pictureunder 4'conditions adjnstetdin accordance with the ratio of lightintensities 'ofthe two said pictures, vand' electrically'transmitting afacsimile of said produced copy.

5.' 'The' method of preparing a 4picture for electrical transmission ofa facsimile thereof which includes optically determining theaveragedensity range'- off said picture, coni-1.

paring the density ran 'e of said picture with' a predetermined sc heuleof density range obtained `from a standard picture hav-ing an-.otimum density range for' electrical facsimi e transmission, reproducingsaid picture to secure a copy thereof having an optimum density-range'varying .between 0.1 and 0.8 and havinga relatively low opacity, andelec?.

trically transmitting a-v facsimile from such copy,` f

standard picture having anoptimum density p range for s electrical`facsimile transmission, reproducing said firstjpictureto 'secure a copythereof having substantially the same density l range as said secondpicture', and-electrically 1 transmitting a .facsimile of said copy.

2. The methodof preparing apicture for` electrical*transmission of -afacsimile thereof, which comprises, opticallyedetermining the densityrange of said picture, comparing said picture with al--predeterminedschedule' of density range obtained from a standard picture havingoptimum density range for electrical facsimile-iitransmission,vreproducing said first picturet o secure a copy thereof havingsubstantially thevs'ame density range as said second named picture', andelectrically' transmitting a' facsimile of said copy.

' Dit.RANGER..

